This invention relates to both fluoroalkanesulfonyl azide compounds which are useful as functional monomers in fluoropolymers and to the fluoropolymers which contain units derived from such fluoroalkanesulfonyl azide monomers.
Fluoroelastomers must generally be cured in order to develop the physical properties necessary for most end use applications. Often, the fluoroelastomer must contain a curesite monomer such as CF2xe2x95x90CFOCF2CF(CF3)OCF2CF2xe2x80x94CN (U.S. Pat. No. 4,281,091) in order to be cured. Such curesite monomers require long exposure to high temperature and the presence of catalyst(s) to complete the curing. However, catalyst residues may adversely affect the properties of the cured fluoroelastomer article, or byproducts of the curing reaction may pose environmental problems. Long exposure to high temperatures may increase manufacturing costs and can cause polymer degradation
Thus, there is a need for curesite monomers which do not require catalysts or long exposure to high temperatures in order to crosslink fluoroelastomers.
There is also a need for fluoropolymers having functional side groups for improving the adhesion of fluoropolymers to other substrates (such as metal surfaces or other polymers), for improved durability of fluoropolymer coatings, and for providing crosslinking to improve the mechanical properties of the fluoropolymers.
The present invention provides a new class of functional monomers having a sulfonyl azide group. Copolymerizing these monomers with at least one other (i.e. different) fluorinated monomer, and (optionally) a fluorine-free monomer, provides a fluoropolymer having a reactive fluoroalkanesulfonyl azide side group which can form crosslinks in fluoropolymers without the need for catalysts or exposure to high temperatures for long periods of time. The sulfonyl azide side group may also be used to enhance adhesion between the fluoropolymer and another substrate, improve the durability of coatings, and increase the mechanical properties of the fluoropolymer through crosslinking.
Specifically, an embodiment of this invention is a fluoroalkanesulfonyl azide compound of the formula
CF2xe2x95x90CFxe2x80x94(O)pxe2x80x94Rfxe2x80x94(CH2)nxe2x80x94S(O)qN3(I)
wherein p=0 or 1; n=0-4; q=1 or 2; and Rf is a C1-C16 perfluoroalkyl or perfluoroalkoxy group. Preferably, p=1; n=0; q=2 and Rf is selected from the group consisting of xe2x80x94CF2CF(CF3)OCF2CF2xe2x80x94 and xe2x80x94(CF2)mxe2x80x94, wherein m=2-4.
A second embodiment of this invention is a fluoroalkanesulfonyl azide compound of the formula
CX1X2xe2x95x90CXxe2x80x94(O)pxe2x80x94Rfxe2x80x94(CH2)nxe2x80x94S(O)qN3xe2x80x83xe2x80x83(II)
wherein X, X1, X2 are independently H or F (with the proviso that X, X1, and X2 can not all be F, so that compound II is not identical to compound I); p=0 or 1; n=0-4; q=1 or 2; and Rf is a perfluoroalkyl or perfluoroalkoxy group. Preferably, X, X1, X2 are H; p=0; n=0; q=2; and Rf is xe2x80x94CF2CF2OCF2CF2xe2x80x94 or xe2x80x94(CF2)yxe2x80x94, wherein y=1-8.
A third embodiment of this invention is a copolymer comprising units derived from compound (I) or compound (II) and units derived from at least one other fluorinated monomer.
It has been discovered that certain fluoroalkylsulfonyl azide compounds are useful as monomers in making fluoropolymers, and are particularly useful in minor amount to introduce highly reactive functional side groups into the fluoropolymer. Such fluoropolymers are useful materials in the areas of curable elastomers and elastoplastics, adhesion enhancement, coatings, thermosetting resins, grafting polymers and the like. Under the appropriate thermal or photo initiation conditions, the sulfonyl azide functional group is able to generate a highly reactive nitrene species. The nitrene intermediate may then undergo either a coupling or an insertion reaction, thereby crosslinking the fluoropolymer chains.
A first embodiment of this invention is a fluoroalkanesulfonyl azide compound of the formula
CF2xe2x95x90CFxe2x80x94(O)pxe2x80x94Rfxe2x80x94(CH2)nxe2x80x94S(O)qN3xe2x80x83xe2x80x83(I)
wherein p=0 or 1; n=0-4; q=1 or 2; and Rf is a C1-C16 perfluoroalkyl or perfluoroalkoxy group. Preferably, p=1; n=0; q=2 and Rf is selected from the group consisting of xe2x80x94CF2CF(CF3)OCF2CF2xe2x80x94 and xe2x80x94(CF2)mxe2x80x94, wherein m=2-4. Specifically, these species include, but are not limited to, CF2xe2x95x90CFOCF2CF(CF3)OCF2CF2xe2x80x94SO2N3 (8-SAVE); CF2xe2x95x90CFOCF2CF2xe2x80x94SO2N3; CF2xe2x95x90CFOCF2CF2CF2xe2x80x94SO2N3; and CF2xe2x95x90CFOCF2CF2CF2CF2xe2x80x94SO2N3.
A second embodiment of this invention is a fluoroalkanesulfonyl azide compound of the formula
CX1X2xe2x95x90CXxe2x80x94(O)pxe2x80x94Rfxe2x80x94(CH2)nxe2x80x94S(O)qN3xe2x80x83xe2x80x83(II)
wherein X, X1, X2 are independently H or F (with the proviso that X, X1 and X2 can not all be F); p=0 or 1; n=0-4; q=1 or 2; and Rf is a perfluoroalkyl or perfluoroalkoxy group. Preferably, X, X1, X2 are H; p=0; n=0; q=2; and Rf is xe2x80x94CF2CF2OCF2CF2xe2x80x94 or xe2x80x94(CF2)yxe2x80x94, wherein y=1-8. A specific example is CH2xe2x95x90CHCF2CF2OCF2CF2xe2x80x94SO2N3.
When q=1 in formula I or II, the monomers of this invention are more correctly described as xe2x80x9cfluoroalkanesulfonyl azidesxe2x80x9d. However, for simplicity, the monomers of this invention are collectively referred to herein as fluoroalkanesulfonyl azides, regardless of whether q=1 or 2.
The general process for making the fluoroalkanesulfonyl azide compounds of this invention is to react sodium azide with the appropriate fluoroalkanesulfonyl fluoride, fluoroalkanesulfonyl bromide, or fluoroalkanesulfonyl chloride at a temperature between xe2x88x9220xc2x0 to 50xc2x0 C. (preferably between 0xc2x0 to 20xc2x0 C.) in a solvent such as methanol, acetonitrile, acetone, or mixtures thereof.
Copolymers of this invention comprise i) units derived from either compound (I) or compound (II) of this invention and ii) units derived from at least one other fluorinated monomer. By xe2x80x9cother fluorinated monomerxe2x80x9d is meant a copolymerizable fluoromonomer other than a fluoroalkanesulfonyl azide. In addition, copolymers may contain units derived from one or more fluorine-free monomers.
Preferably, units derived from compound (I) or compound (II) are present in minor amounts in the copolymers of this invention. Typically, copolymers contain 0.02-10 mole percent (based on the total monomer units in the polymer) of units derived from either compound (I) or compound (II), preferably 0.1-5 mole percent and most preferably 0.3-3 mole percent.
Fluorinated monomers suitable for forming copolymers with compound (I) or compound (II) include, but are not limited to: tetrafluoroethylene (TFE); chlorotrifluoroethylene (CTFE); trifluoroethylene; vinylidene fluoride (VF2); vinyl fluoride (VF); hexfluoropropylene (HFP); 1- or 2-hydropentafluoropropylene, 3,3,3-trifluoropropylene; hexafluoroisobutylene; perfluoro(alkyl vinyl ethers) (PAVE) having alkyl groups containing 1-5 carbon atoms (preferably 1-3 carbon atoms); perfluoro(alkoxy vinyl ethers) having alkoxy groups containing 1-5 carbon atoms; perfluoro-(2,2-dimethyl-1,3-dioxole) (PDD) and perfluoro-(2-methylene-4-methyl-1,3-dioxolane) (PMD). Also included in this group of fluorinated monomers are perfluoro(alkyl vinyl ethers) which contain functional groups such as acid fluorides or esters. Examples of these ethers include CF2xe2x95x90CFOCF2CF(CF3)OCF2CF2SO2F (PSEPVE) and CF2xe2x95x90CFOCF2CF(CF3)OCF2CF2COOCH3 (EVE). Preferably, at least one of the fluorinated monomers is selected from the group consisting of TFE, CTFE and VF2.
Fluorine free monomers that can be used in the copolymers of this invention include: ethylene, propylene, n-butylene, iso-butylene, vinyl acetate (VAc), and vinyl ethers such as methyl vinyl ether.
The copolymers of this invention may be glassy, thermoplastic or elastomeric. They may be amorphous or partially crystalline, melt-fabricable or non-melt-fabricable. One skilled in the art will readily recognize that such polymer properties are controlled by the type of monomers used in the copolymer and their relative levels.
Typical elastomeric copolymers of this invention comprise, in addition to minor amounts of units derived from either compound (I) or compound (II), units derived from a combination of monomers selected from the group consisting of a) VF2 and HFP; b) VF2, HFP and TFE; c) VF2, PAVE and TFE; d) TFE and PAVE; e) TFE and propylene; f) TFE, VF2 and propylene; and g) TFE, PAVE and ethylene.
Typical thermoplastic copolymers of this invention comprise, in addition to units derived from either compound (I) or compound (II), units derived from either TFE or CTFE and up to 10 mole percent of one or more additional monomers such as HFP, PDD, PMD and ethylene.
Copolymers of this invention may be prepared by any of the known processes for producing fluoropolymers. Such processes may be conducted, for example, in an aqueous or non-aqueous medium, or in mixed media as is well known in the art. As is likewise well known in the art, dispersion, emulsion, solution or suspension processes may be employed, and the processes may be conducted on a continuous, batch or semi-batch basis.
The copolymer emerging from the reactor may be isolated and dried by any known technique, taking care that the polymer is not heated enough to cause crosslinking. Alternatively, an aqueous dispersion emerging from the reactor may be used directly as-is, for example as a coating composition, or it may first be stabilized by addition of surfactant and/or concentrated by processes well known in the art for the preparation of latex coating compositions.
Copolymers of this invention may be cured by exposure to UV radiation or heat. In addition, copolymers of this invention may be mixed with other curable polymers and curing agents and the resulting mixture co-cured. The copolymers of this invention may also be mixed with additives, processing aids and fillers well known in the rubber and plastics industries such as, but not limited to, carbon black, mineral fillers including barium sulfate, talc and silica, fibrillating or non-fibrillating thermoplastic fluoropolymers, metal oxides, metal hydroxides and the like.